Transferring dyes for thermal printing

ABSTRACT

Dyes are transferred from a carrier by sublimation/vaporization to plastic-coated papers by a process in which the dyes used are of the general formula (I) ##STR1## where A is D--N=N-- or ##STR2## R 1  and R 2  are each hydrogen, alkyl, alkoxy, alkylthio or halogen and R 1  and R together may furthermore form a 5-membered or 6-membered heterocyclic ring, and R and R&#39; independently of one another are each hydrogen, phenyl which is unsubstituted or substituted by methyl or methoxy, or C 5  - or C 6  -cycloalkyl or C 1  -C 6  -alkyl which is unsubstituted or substituted by C 1  -C 4  -alkoxy, C 1  -C 4  -alkoxycarbonyl, C 2  -C 5  -alkanoyloxy, C 1  -C 4  -alkoxycarbonyloxy, C 1  -C 4  -alkoxy-C 2  - or C 3  -alkoxycarbonyloxy, hydroxyl, cyano, halogen, phenyl or C 5  - or C 6  cycloalkyl, or ##STR3## is a 5-membered or 6-membered saturated heterocyclic ring where D is a radical of a diazo component of the thiophene, thiazole, isothiazole or 1,2,4-thiadiazole series and R 3  is hydrogen or CN. 
     In the process, the dyes (I) give strong dyeings which have good light fastness and are resistant to chemical substances.

This is a division of application Ser. No. 384,095, filed on Jul. 24, 1989now U.S. Pat. No. 4,999,026, which is a continuation of application Ser. No. 228,874, filed Aug. 5, 1988, now abandoned, which is a continuation of Ser. No. 089,542, filed Aug. 26, 1987, now abandoned.

In the sublimation transfer process, a transfer sheet which contains a sublimable dye with or without a binder on a carrier is heated from the rear by short heat pulses (lasting fractions of a second) using a thermal printing head, the dye being sublimed or vaporized and transferred to a receiving medium. The essential advantage of this process is that the amount of dye to be transferred (and hence the color gradation) can readily be controlled by adjusting the energy to be supplied to the thermal printing head.

In general, the color image is produced using the three subtractive primary colors, yellow, magenta and cyan (and if necessary black). In order to permit an optimum color image to be produced, the dyes must have the following properties:

i) readily sublimable or vaporizable; in general, this requirement is most difficult to meet in the case of the cyan dyes;

ii) high thermal and photochemical stability and resistance to moisture and chemical substances;

iii) suitable hues for subtractive color mixing;

iv) a high molecular absorption coefficient;

v) readily obtainable industrially.

Most of the known dyes used for thermal transfer printing do not adequately meet these requirements.

The prior art discloses dyes for this purpose.

JP-A 159091/1985 describes dyes of the formula ##STR4## where R is alkyl, aralkyl, aryl or a 5-membered or 6-membered carbocyclic ring, for this purpose.

JP-A 30392/1985 discloses dyes of the formula ##STR5## where R, R¹ and R² are each allyl, alkyl or alkoxyalkyl and X is H or methyl.

JP-A 229786/1985 describes dyes of the formula ##STR6## where R and R¹ are each methyl, ethyl, propyl or butyl and X is H or methyl, for this application. In JP-A 239292/1985, dyes of the formula ##STR7## are described for the transfer process. In the formula, R¹ is C₁ -C₈ -alkyl, R² is H or methyl and D is ##STR8##

Quinone derivatives of the formula ##STR9## where R and R¹ are each methyl, ethyl, propyl or butyl, are described for this application in JP-A 229 786/1985.

Furthermore, the use of indoaniline dyes of the general formula ##STR10## is described for this purpose in DE-A 35 24 519.

It is an object of the present invention to provide dyes which are readily sublimable or vaporizable under the conditions produced by a thermal printing head, do not undergo thermal or photochemical decomposition, can be processed to give printing inks and meet the color requirements. The dyes should also be readily obtainable industrially.

We have found that this object is achieved by a process for transferring dyes from a carrier by sublimation/vaporization with the aid of a thermal printing head to a plastic-coated paper, wherein a carrier is used on which dyes of the general formula ##STR11## where A is D--N═N-- or ##STR12## R¹ and R² independently of one another are each hydrogen, C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy, C₁ -C₄ -alkylthio or halogen and R¹ together with R may form a 5-membered or 6-membered heterocyclic ring, and R and R' independently of one another are each hydrogen, phenyl which is unsubstituted or substituted by methyl or methoxy, or C₅ - or C₆ -cycloalkyl or C₁ -C₆ -alkyl which is unsubstituted or substituted by C₁ -C₄ -alkoxy, C₁ -C₄ -alkoxycarbonyl, C₂ -C₅ -alkanoyloxy, C₁ -C₄ -alkoxycarbonyloxy, C₁ -C₄ -alkoxy-C₂ - or C₃ -alkoxycarbonyloxy, hydroxyl, cyano, halogen, phenyl or C₅ - or C₆ -cycloalkyl, or ##STR13## is a 5-membered or 6-membered heterocyclic ring, D is ##STR14## R³ is hydrogen or CN, R⁴ is C₁ -C₄ -alkyl, phenyl, benzyl or CN, R⁵ is C₁ -C₄ -alkyl, C₁ -C₄ -alkylthio, C₁ -C₄ -alkoxy, C₅ - or C₆ -cycloalkyl, benzyl, C₅ - or C₆ -cycloalkylthio, C₅ - or C₆ -cycloalkoxy, benzyloxy or benzylthio, R⁶ is CN or --CHO, R⁷ is C₁ -C₄ -alkoxy, C₁ -C₄ -alkylthio or chlorine and R⁸ is --CHO, CN or nitro, and R¹ and R² must not be hydrogen when A is ##STR15## and R⁵ is alkylthio or when A is ##STR16##

Compared with the dyes used in the conventional processes, those employed in the novel process possess better sublimability and in some cases greater lightfastness and greater resistance to chemical substances.

In the process of the invention, dyes of the general formula ##STR17## are used. In the formula, A is D--N═N-- or ##STR18##

In addition to being hydrogen, R¹ and R² are, for example, C₁ -C₄ -alkyl, such as CH₃, C₂ H₅, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl, C₁ -C₄ -alkoxy, such as methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy or tert-butoxy, C₁ -C₄ -alkylthio, such as methylthio, ethylthio or butylthio or halogen, such as bromine, but preferably chlorine or fluorine. R¹ together with R may furthermore form a heterocyclic ring, so that ##STR19## can correspond to the following formulae: ##STR20##

In the formulae (I) and (IIa) to (IId), R and R' independently of one another are each hydrogen or C₁ -C₆ -alkyl which is unsubstituted or substituted by C₁ -C₄ -alkoxy, C₁ -C₄ -alkoxycarbonyl, C₁ -C₄ -alkoxycarbonyloxy, C₂ -C₅ -alkanoyloxy, C₁ -C₄ -alkoxy-C₂ - or C₃ -alkoxycarbonyloxy, hydroxyl, cyano, halogen, phenyl or C₅ - or C₆ -cycloalkyl.

Specific examples of C₁ -C₆ -alkyl are methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, n-hexyl and isohexyl.

Specific examples of C₁ -C₄ -alkoxy in the alkoxy-carrying substituents are methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy and isobutoxy.

Suitable halogen substituents on C₁ -C₆ -alkyl are bromine, chlorine and preferably fluorine.

Specific examples of C₂ -C₅ -alkanoyl are acetyl, propionyl, butanoyl and pentanoyl.

R' and R may furthermore be phenyl which is unsubstituted or substituted by methyl or methoxy, or may be C₅ - or C₆ -cycloalkyl or benzyl.

Specific examples of substituted C₁ -C₆ -alkyl are 2-hydroxyethyl, 2- and 3-hydroxypropyl, 3- and 4-hydroxybutyl, 2-cyanoethyl, 3-cyanopropyl and 4-cyanobutyl, benzyl, 2-phenylethyl and 2- and 3-phenylpropyl, methoxyethyl, 2- and 3-methoxypropyl, ethoxyethyl, n- and isopropoxyethyl and n- and isobutoxyethyl, 2-acetoxyethyl, 2-propanoyloxyethyl, 2-butanoyloxyethyl and 2-pentanoyloxyethyl, 2- and 3-acetoxypropyl, 2- and 3-propanoyloxypropyl, 2- and 3-butanoyloxypropyl and 2- and 3-pentanoyloxypropyl, 2-(methoxycarbonyl)-ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyl)-ethyl, 2-(butoxycarbonyl)ethyl and the corresponding 3-propyl derivatives, 2-(methoxycarbonyloxy)-ethyl, 2-(ethoxycarbonyloxy)-ethyl, 2-(n- and isopropoxycarbonyloxy)-ethyl, 2-(n- and isobutoxycarbonyloxy)-ethyl and the corresponding 3-(alkoxycarbonyloxy)-propyl derivatives, 2-(methoxyethoxycarbonyloxy)-ethyl, 2-(ethoxyethoxycarbonyloxy)-ethyl, 2-(n- and isopropoxyethoxycarbonyloxy)-ethyl and 2-(n- and isobutoxyethoxycarbonyloxy)-ethyl and the corresponding 3-(alkoxyalkoxycarbonyloxy)-propyl derivatives, and cyclopentylmethyl and cyclohexylmethyl.

Unsubstituted or substituted phenyl radicals R and R' are phenyl as well as 2- and 4-methylphenyl and 2- and 4-methoxyphenyl. Where R is phenyl or substituted phenyl, R' is preferably methyl and in particular hydrogen. ##STR21## may furthermore be a heterocyclic radical, such as ##STR22##

R³ is hydrogen or CN.

D is a radical of the formula ##STR23## where R⁴ is C₁ -C₄ -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, phenyl, benzyl or CN, R⁵ is C₁ -C₄ -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, or tert-butyl, C₁ -C₄ -alkoxy, such as methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy or tert-butoxy, C₁ -C₄ -alkylthio, benzyl, C5- or C6-cycloalkyl, C₅ - or C₆ -cycloalkylthio, C₅ - or C₆ - cycloalkoxy, benzyloxy or benzylthio, R⁶ is CN or --CHO, R⁷ is C₁ -C₄ -alkoxy, such as methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy, or tert-butoxy, C₁ -C₄ -alkylthio or chlorine, and R⁸ is --CHO, CN or nitro.

Dyes (I) in which A is ##STR24## and R⁵ is alkylthio or A is ##STR25## are excluded when R¹ and R² are each hydrogen.

The following are preferred for the present process:

a) Dyes of the formula (I) where R and R' are each hydrogen or C₁ -C₄ -alkyl which is unsubstituted or substituted by hydroxyl, cyano or phenyl, or are each C₁ -C₄ -alkoxy-C2-C4-alkyl, C₁ -C₄ -alkoxycarbonyl-C₁ -C₄ -alkyl, C₁ -C₄ -alkoxycarbonyloxy-C₂ -C₄ -alkyl or C₁ -C₄ -fluoroalkyl, or phenyl which is unsubstituted or substituted by methoxy or methyl, R¹ and R² are each hydrogen, methyl, methoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy or tert-butoxy

and A is D--N═N-- or ##STR26## and where D is ##STR27## where R⁴ is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl or cyano and R⁵ is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, methylthio, ethylthio, n-propylthio, isopropylthio, n-butylthio, isobutylthio or tert-butylthio.

b) Dyes of the formulae ##STR28## where D is ##STR29## R⁴ is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl or CN, R⁵ is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, methylthio, ethylthio, n-propylthio, isopropylthio, n-butylthio, isobutylthio or tert-butylthio and R is hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl.

Particularly preferred dyes are those of the formula ##STR30## where R⁹ is hydrogen, C₁ -C₄ -alkoxy, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy or tertbutoxy, R¹⁰ and R¹¹ independently of one another are each hydrogen, C₁ -C₄ -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl, C₁ -C₄ -alkoxycarbonylethyl or C₂ -C₅ -alkanoyloxyethyl, and those of the formulae (IIIa), (IIIb), (IIIc) and (IIId) where D is ##STR31## and R is hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl.

Other particularly preferred dyes are those of the formula ##STR32## where R and R' independently of one another are each hydrogen, C₁ -C₄ -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl, phenyl, C₂ -C5-alkanoyloxyethyl, C₁ -C₄ -alkoxycarbonylethyl, C₁ -C₄ -alkoxycarbonyloxyethyl, benzyl or cyanoethyl, R¹ and R² independently of one another are each hydrogen, C₁ -C₄ -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl, C₁ -C₄ -alkoxy, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy or tert-butoxy, or C₁ -C₄ -thioalkyl, and R⁴ is C₁ -C₄ -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl, or phenyl.

The dyes (I) are synthesized by conventional processes or processes known per se.

Azo dyes of the general formula (V) where R, R' , R¹, R² and R⁴ have the stated meanings, are prepared by the process described in German Laid-Open Application DOS 3,207,290. The diazo component (R⁴ =CN) ##STR33## is disclosed in DE-A 34 02 024. Azo dyes (I) where D is ##STR34## and R⁵ is alkylthio have been synthesized by the process described in DE-C 15 44 391. Diazo components where R⁵ is alkyl have been prepared by the synthesis described in Chem. Ber. 87 (1954), 57.

Azo dyes (I) where D is ##STR35## have been synthesized by the process described in DE-A 31 08 077 and 35 29 831, respectively.

Dyes of the type ##STR36## have been prepared by the process described by McKusick et al., J. Am. Chem. Soc. 80 (1958), 2806, by reacting the corresponding aniline derivatives with tetracyanoethylene.

Dyes (I) in which A is ##STR37## have been obtained by known processes, by reacting appropriate p-formylanilines with malodinitrile.

To prepare the dye carriers required for the process, the dyes in a suitable solvent, eg. chlorobenzene or isobutanol, are processed with a binder to give a printing ink. The latter contains the dye in dissolved or dispersed form. The printing ink is applied to the inert carrier by means of a knife coater, and the dying is dried in the air. Examples of suitable binders are ethylcellulose, polysulfones and polyethersulfones. Examples of inert carriers are tissue paper, blotting paper and glassine, as well as plastic films possessing good heat stability, for example uncoated or metal-coated polyester, nylon or polyimide. The carrier is preferably from 3 to 30 μm thick. Other carriers suitable for the novel process and binders and solvents for the preparation of the printing inks are described in DE-A 35 24 519.

Suitable dye-accepting layers are in principle all heat-stable plastic layers possessing an affinity for the dyes to be transferred, eg. polyesters.

Transfer is effected by means of a thermal printing head, which must supply sufficient heating power to transfer the dye within a few milliseconds.

The embodiments which follow are intended to illustrate the invention further.

In order to be able to test the transfer behavior of the dyes quantitatively and in a simple manner, the thermal transfer is carried out using heating jaws having a large area, instead of a thermal printing head, and the dye carriers to be tested are prepared without the use of a binder.

A) General formulations for coating the carriers with dye:

AI)

1 g of ethylene glycol,

1 g of dispersant based on a condensate of phenol, formaldehyde and Na bisulfite,

7.5 g of water and

0.5 g of dye, together with

10 g of glass spheres (2 mm diameter)

are introduced into vessels and the latter are closed and shaken on a shaking apparatus (Red Devil®) until the mean particle size of the dye is ≦1 μm (duration: from 8 to 12 hours, depending on the dye). The glass spheres are separated off by means of a sieve and the resulting dye dispersion, which may be diluted with water to twice its volume, is applied to paper using a 6 μm knife coater and dried in the air.

AII) The dye is applied to the paper carrier once or several times in the form of a solution having a saturation of about 90% in a solvent (eg. chlorobenzene, tetrahydrofuran, methyl ethyl ketone, isobutanol or a mixture of these) by the spin-coating method. The amount of dye applied by spin coating is adjusted so that, on complete transfer to an 80 μm thick polyester film (acceptor), an extinction of not less than 2 is obtained.

B) Testing the sublimation/vaporization behavior

The dyes used were tested in the following manner: The paper layer (donor) coated with the dye to be tested is placed with the dye layer on an 80 μm thick polyester film (acceptor) and pressed against it. The donor and acceptor are then wrapped with aluminum foil and heated for 30 seconds between two heated plates. The amount of dye which has migrated to the polyester film is determined photometrically. If the logarithm of the extinction A of the dyed polyester films measured at various temperatures (range: 100°-200° C.) is plotted against the associated reciprocal absolute temperature, straight lines are obtained from whose slope the activation energy ΔE_(T) for the transfer experiment is calculated: ##EQU1##

For complete characterization, the temperature T* [°C] at which the extinction A of the dyed polyester film reaches the value 1 is additionally obtained from the plots.

EXAMPLES 1 TO 27

The dyes stated in Tables 1 to 6 were processed according to AI) or AII), and the sublimation behavior of the resulting dye-coated carriers was tested according to B). The Table lists the hue on polyester and the thermal transfer parameters T* and ΔE_(T).

                                      TABLE 1                                      __________________________________________________________________________      ##STR38##                                                                      Example                                                                             X                      Hue  T*[°C.]                                                                     ##STR39##                                __________________________________________________________________________      1                                                                                   ##STR40##             magenta                                                                             145 23                                         2                                                                                   ##STR41##             violet                                                                              156 16                                         3                                                                                   ##STR42##             magenta                                                                             153 18                                         4                                                                                   ##STR43##             violet                                                                              174 23                                         5                                                                                   ##STR44##             magenta                                                                             165 25                                         6                                                                                   ##STR45##             magenta                                                                             156 21                                         7                                                                                   ##STR46##             magenta                                                                             154 17                                         8                                                                                   ##STR47##             magenta                                                                             161 19                                         9                                                                                   ##STR48##             magenta                                                                             155 21                                        10                                                                                   ##STR49##             magenta                                                                             169 17                                        11                                                                                   ##STR50##             magenta                                                                             157 17                                        12                                                                                   ##STR51##             magenta                                                                             173 20                                        13                                                                                   ##STR52##             magenta                                                                             151 21                                        14                                                                                   ##STR53##             red  170 20                                        15                                                                                   ##STR54##             magenta                                                                             175 20                                        16                                                                                   ##STR55##             magenta                                                                             162 19                                        17                                                                                   ##STR56##             magenta                                                                             171 20                                        __________________________________________________________________________

                                      TABLE 1a                                     __________________________________________________________________________      ##STR57##                                                                      Example                                                                             X                        Hue     T*[°C.]                                                                     ##STR58##                           __________________________________________________________________________     18                                                                                   ##STR59##               yellow  190                                      19                                                                                   ##STR60##               greenish yellow                                                                        121 26                                   20                                                                                   ##STR61##               yellow  120 23                                   21                                                                                   ##STR62##               yellow  120 25                                   22                                                                                   ##STR63##               yellow  130 23                                   23                                                                                   ##STR64##               yellow  158 24                                   24                                                                                   ##STR65##               yellow  157 24                                   25                                                                                   ##STR66##               reddish yellow                                                                         130 20                                   26                                                                                   ##STR67##               yellow  154 24                                   27                                                                                   ##STR68##               yellow  152 21                                   __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________      ##STR69##                                                                      Example                                                                              R.sup.4                                                                               X                            Hue     T*[°C.]                                                                      ##STR70##              __________________________________________________________________________     28    CH.sub.3                                                                               ##STR71##                   magenta 148  17                      29    CH.sub.3                                                                               ##STR72##                   magenta 175  18                      30                                                                                    ##STR73##                                                                             ##STR74##                   magenta 155  19                      31                                                                                    ##STR75##                                                                             ##STR76##                   magenta 149  19                      32    CH.sub.3                                                                               ##STR77##                   magenta 134  23                      33    CH.sub.3                                                                               ##STR78##                   magenta 140  25                      34    CH.sub.3                                                                               ##STR79##                   magenta 141  23                      35    CH.sub.3                                                                               ##STR80##                   red     140  25                      36    CH.sub.3                                                                               ##STR81##                   red     178  17                      37    CH.sub.3                                                                               ##STR82##                   magenta 173  16                      38                                                                                    ##STR83##                                                                             ##STR84##                   magenta 172  28                      39                                                                                    ##STR85##                                                                             ##STR86##                   magenta-violet                                                                         200  19                      40    CH(CH.sub.3).sub.2                                                                     ##STR87##                   magenta 164  16                      41    CH.sub.3                                                                               ##STR88##                   magenta 167  16                      42    CH.sub.3                                                                               ##STR89##                   magenta 161  25                      43    CH.sub.3                                                                               ##STR90##                   magenta 155  23                      44    CH.sub.3                                                                               ##STR91##                   red     167  25                      45    CH.sub.3                                                                               ##STR92##                   magenta 164  25                      46    CH.sub.3                                                                               ##STR93##                   magenta 190  32                      47    CH.sub.3                                                                               ##STR94##                   magenta 199  31                      48    CH.sub.3                                                                               ##STR95##                   magenta 193  30                      49    CH.sub.3                                                                               ##STR96##                   magenta 177  26                      50    CH(CH.sub.3).sub.2                                                                     ##STR97##                   magenta 193  31                      51    CH(CH.sub.3).sub.2                                                                     ##STR98##                   magenta 199  24                      52    CH.sub.3                                                                               ##STR99##                   magenta 154  25                      __________________________________________________________________________

                                      TABLE 3                                      __________________________________________________________________________      ##STR100##                                                                     Example                                                                             R.sup.5                                                                             X            Hue                                                                                T*[°C.]                                                                     ##STR101##                                     __________________________________________________________________________     53   CH.sub.3                                                                             ##STR102##  reddish                                                                            155 20                                              54   SCH.sub.3                                                                            ##STR103##  reddish                                                                            162 21                                              55   CH.sub.3                                                                             ##STR104##  violet                                                                             172 23                                              56   CH.sub.3                                                                             ##STR105##  violet                                                                             170 22                                              __________________________________________________________________________

                  TABLE 4                                                          ______________________________________                                          ##STR106##                                                                     pleExam-                                                                             X                Hue     [°C.]T*                                                                      ##STR107##                                ______________________________________                                         57                                                                                    ##STR108##      violet  180  20                                         58                                                                                    ##STR109##      violet  172  19                                         59                                                                                    ##STR110##      reddish blue                                                                           176  20                                         ______________________________________                                    

                                      TABLE 5                                      __________________________________________________________________________      Example                                                                             X                       Hue                                                                               T*[°C.]                                                                     ##STR111##                                __________________________________________________________________________     60                                                                                   ##STR112##             blue                                                                              170 25                                         __________________________________________________________________________

                                      TABLE 6                                      __________________________________________________________________________      ##STR113##                                                                     Example                                                                             X                   Hue    T*[°C.]                                                                      ##STR114##                               __________________________________________________________________________     61                                                                                   ##STR115##         reddish blue                                                                          172  24                                        62                                                                                   ##STR116##         reddish blue                                                                          180  23                                        63                                                                                   ##STR117##         reddish blue                                                                          178  23                                        64                                                                                   ##STR118##         cyan   165  25                                        65                                                                                   ##STR119##         cyan   170  27                                        66                                                                                   ##STR120##         cyan   175  27                                        67                                                                                   ##STR121##         blue   169  24                                        68                                                                                   ##STR122##         cyan   192  26                                        69                                                                                   ##STR123##         cyan   182  25                                        70                                                                                   ##STR124##         reddish blue                                                                          169  29                                        71                                                                                   ##STR125##         reddish blue                                                                          173  34                                        72                                                                                   ##STR126##         reddish blue                                                                          179  32                                        73                                                                                   ##STR127##         neutral blue                                                                          163  28                                        74                                                                                   ##STR128##         reddish blue                                                                          159  21                                        75                                                                                   ##STR129##         reddish blue                                                                          165  30                                        76                                                                                   ##STR130##         reddish blue                                                                          166  25                                        77                                                                                   ##STR131##         violet 185  25                                        78                                                                                   ##STR132##         neutral blue                                                                          178  26                                        79                                                                                   ##STR133##         neutral blue                                                                          177  27                                        80                                                                                   ##STR134##         cyan   174  26                                        __________________________________________________________________________

In the case of the dye of Example 23, samples were heated as described in B) to the temperatures stated in Table 6, in each case for 30 seconds, after which the extinction of the dyeing on polyester was determined. The extinctions and temperatures for 6 measured points are stated in Table 7.

                  TABLE 7                                                          ______________________________________                                         Sample                                                                               20.1     20.2    20.3   20.4  20.5   20.6                                ______________________________________                                         t° C.                                                                         137      146     154    158   168    176                                 A     0.137    0.247   0.435  0.659 1.094  2.08                                ______________________________________                                    

In FIG. 1, the values are plotted in the form of log A against ##EQU2##

In the graph, ΔLog A=1.14 when ##EQU3## from which ΔE_(T) can be calculated: ##EQU4##

The graph furthermore gives ##EQU5## 

We claim:
 1. A process for transferring a dye from a carrier by sublimation/-vaporization with the aid of a thermal printing head to a plastic-coated paper, said carrier employing a dye of the formula:where R¹ is, C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy, C₁ -C₄ -alkylthio or halogen and R¹ together with R may form a 5-membered or 6-membered heterocyclic ring, and R and R' independently of one another are each hydrogen, phenyl which is unsubstituted or substituted by methyl or methoxy, or C_(5-C) ₆ -cycloalkyl or C_(1-C) ₆ -alkyl, which is unsubstituted or substituted by C₁ -C₄ -alkoxy, C₁ -C₄ -alkoxycarbonyl, C₂ -C₅ -alkanoyloxy, C₁ -C₄ -alkoxycarbonyloxy, C₁ -C₄ -alkoxy-C₂ - or C₃ -alkoxycarbonyloxy, hydroxyl, cyano, halogen, phenyl or C₅ - or C₆ -cycloalkyl, or is a 5-membered or 6-membered heterocyclic ring, D is ##STR135## R⁷ is chlorine and R⁸ is --CHO, CN or nitro.
 2. The process as claimed in claim 1, wherein R and R' independently of one another are each hydrogen or C₁ -C₄ -alkyl which is unsubstituted or substituted by hydroxyl, cyano or phenyl, or are each C₁ -C₄ -alkoxy-C₂ -C₄ -alkyl, C₁ -C₄ -alkoxycarbonyl-C₁ -C₄ -alkyl, C₁ -C₄ -alkoxycarbonyl-oxy-C₂ -C₄ -alkyl or C₁ -C₄ -fluoroalkyl, R¹ is C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy or C₁ -C₄ -alkylthio.
 3. The process as claimed in claim 1 where D is ##STR136## and R⁴ is C₁ -C₄ -alkyl, phenyl, benzyl or CN.
 4. The process as claimed in claim 2 where D is R1 ? ##STR137##
 5. The process as claimed in claim 1, wherein a dye of the formula: ##STR138## is used, where R⁹ is C₁ -C₄ -alkoxy and R¹⁰ and R¹¹ independently of one another are each hydrogen, C₁ -C₄ -alkyl, C₁ -C₄ -alkoxycarbonylethyl or C₂ -C₅ -alkanoylethyl. 